The effective connection between cellular tissues and technological platforms is crucial for the success of many bionic applications as neural prostheses and hybrids for studying information processing in neuronal networks. Moreover, the recent attention for disposable, low-cost and reliable cell-to-chip interface systems for high-throughput in-vitro toxicity assays and pharmacology is becoming an urgent request because of the new international regulatory test guidelines (both in Europe and USA). Therefore, engineering the so-called bio-electronic interface is the subject of many technological and basic/applied researches. Specifically related to the cell (neuronal)-electronic interface, two different kinds of devices have been extensively used over the past thirty years, namely microelectrodes arrays and field-effect devices.
More recently, organic semiconductors have attracted a considerable interest in this field (see for example Simon D. T. et al, Nature Material 8, 742-746 (2009)) because they have the potential to fulfill many critical requirements for biomedical and biotechnological applications such as biological compatibility, mechanical flexibility, and optical transparency. Moreover, devices based on organic semiconductors can be fabricated on flexible low-cost plastic substrates, with micrometric resolution, over large areas, and using cost-efficient technologies. All these features could allow addressing a wide variety of novel applications ranging from in-vitro to in-vivo cell biology and addressing unsolved problems of mechanical adaptability (e.g., high density flexible transducers on catheters) or of multi-parameters analysis on a micro-scale (e.g., disposable and sensorized smart-Petri dish). So far, in addition to passive electrodes made of organic conductive polymers, organic electrochemical transistors (OECTs) have been mainly proposed (See e.g. Khodagholy et al. Nature Communication, 4 (2013)) because of their ability to conduct ionic and electronic charges and to be operated in liquid at very low voltages, which represents a crucial requirement in presence of living cells or tissues. Organic Thin Film Transistors (OTFTs) have not yet been employed so far to this aim for two main reasons: 1) they usually need to be operated at relatively high voltages (usually tens of volts); 2) charge carrier mobility in organic semiconductors is generally orders of magnitude smaller than what generally measured in their standard inorganic counterparts, putting a limit on the frequency range of the electrical signals that might be applied as input for organic amplifiers.
A very recent attempt has been done (Benfenati et al. Nature Material, 12, 672-680 (2013)) but, as a matter of fact, the organic transistor employed in the reported experiments is always operated in the off-state and therefore, this cannot be described as an actual amplifying transducer for the cell activity.